They've been admitted to EU so women there are free to roam around Europe, to where the grass in greener (the West, or I should say the real Europe).
Judging by their written English, they probably live in the West and have experience dealing with white women in their home countries.
So there you go, you should know how to set your expectations.
Anyways I was only in Minsk for a few days, I can't really say.
I saw maybe just one or two non white people there, and Minsk is not a small city. But I'd think skin color doesn't matter much to pros. Minsk isn't the best place for seeing pros, but it could be a great place for freebies if you live there.
Some of them are hookers and private escorts looking for a quick lay with a tourist.